Oral Presentation Skin Cancer 2024

The genomic landscape of melanoma-prone skin (#102)

Katie J Lee 1 2 , Wendy Kao 1 , Darren Smit 1 , Marietta K Saldias Montivero 3 , Brock C Christensen 3 , Quan Nguyen 4 , Peter Soyer 1 , Mitchell S Stark 1
  1. Dermatology Research Centre, The University of Queensland Frazer Institute, Brisbane, Qld, Australia
  2. The University of Queensland Frazer Institute, Coorparoo, QLD, Australia
  3. Geisel School of Medicine, Hannover, New Hampshire, USA
  4. QIMR Berghofer Medical Research Institute, Brisbane, Qld, Australia

Normal skin carries a high burden of somatic mutations, yet this does not explain where a melanoma will form. The PhotoMelanoma Study aimed to determine the genomic architecture of the microenvironment that favours melanoma formation. We invited 19 study participants from a high-risk melanoma cohort to donate three biopsies each: photodamaged skin adjacent to an invasive melanoma excision, photodamaged skin 5cm away, and photoprotected skin. Biopsies were assessed for hotspot mutations via droplet digital PCR; somatic mutation burden, mutation signature, and copy number aberrations via deep panel sequencing (PanelSeq), and global methylation profiling. BRAF, NRAS, and TERT promoter (TERTp) driver mutations were detected in all biopsy sites with no statistical enrichment in photodamaged or scar sites. This suggests that these mutations arise post-zygosis and are not UV-induced. The mitochondrial ‘common deletion’ was significantly more common in aged photodamaged skin, in keeping with prior studies. PanelSeq showed UV-related mutation signature (SBS7) at levels similar across sun-exposed sites, whereas signature SBS2 was enriched (67%) at scar-adjacent sites only. Lastly, global DNA methylation profiling identified 2000+ loci differentially methylated between photodamaged and photoprotected sites, including HOX family members with roles in cell positioning. In sum, contrary to our initial hypothesis, BRAF, NRAS, and TERTp driver mutations and mitochondrial common deletion were not enriched at the melanoma scar-adjacent site. There were differences in mutation signatures, with SBS2 enrichment potentially influenced by viral infections, transposable elements or inflammation. These data are part of a comprehensive genomic profile to identify the underlying causes of melanoma development.